Oven doors are constructed to retain heat inside an oven cavity. Typically, oven doors are made using inner and outer door panels positioned in a parallel, spaced-apart relationship and joined together at the edges to form therebetween an interior region. The inner panel, facing the interior of the oven, absorbs large amounts of heat, which is transferred to the outer panel by conduction, radiation, and convection. It is desirable to limit the temperature rise of the outside surface of the door and to avoid hot spots of excessive temperature. Underwriters' Laboratories, Inc. has specified a limit of 152.degree. F. for the acceptable temperature for a stainless steel outer door panel. Maintaining the entire outside surface of an oven door at 152.degree. F. or less is frequently difficult. In self-cleaning ovens the temperature within the oven can reach 950.degree. F. during the cleaning process. At that temperature, much heat is transferred through the inner panel to the outer panel, and the outer door surface can be heated beyond an acceptable temperature without means for reducing the temperature of outside surface of the door.
One method known in the art for reducing the surface temperature of the outer panel is the use of convective heat transfer. In using convective heat transfer, apertures are formed in the top and bottom of the outer panel of the door. Warm air from the interior region between the inner and outer panels of the door rises through the apertures formed in the top of the outer door panel and draws cooling air from outside of the oven up into the interior region through the apertures in the bottom of the door. As the cooling air travels through the interior region, it picks up heat from the outer door panel and carries it away to the atmosphere, thereby cooling the outer door panel.
It is desirable to be able to observe, from time to time, the interior of the oven. To permit visual inspection without the necessity of opening the oven door and thereby losing heat to the atmosphere, it is known to install glass panels in the oven door. See, for example, U.S. Pat. No. 3,939,817 to Nuss. Nuss discloses an oven door having a glass viewing window in the outer panel and cooling air channels which allow room air to pass up through the door.
Underwriters' Laboratories, Inc. has specified a 172.degree. F. limit for the acceptable surface temperature for glass, which is the preferred material for use as a viewing window. To meet the 172.degree. F. limit, thermally insulating viewing window assemblies have been developed. Such assemblies include multiple glass panes separated by insulative air gaps and sealed into a unit. Unfortunately, when installed in the door, the window elements can block the flow of cooling air through the door and cause localized areas of increased temperature, ("hot spots") in the outer panel, particularly in the area of the outer panel above the viewing window assembly. It has long been a desire that oven doors be provided with means for eliminating localized areas of excessive temperature and, particularly for eliminating "hot spots" caused by insulative viewing windows of oven doors.